Single-Table NoSQL In-Memory Database

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This Ruby gem manages an in-memory database of facts. A fact is simply a map of properties and values. The values are either atomic literals or non-empty sets of literals. It is possible to delete a fact, but impossible to delete a property from a fact.

ATTENTION: The current implemention is naive and, because of that, very slow. I will be very happy if you suggest a better implementation without the change of the interface. The Factbase::query() method is what mostly needs performance optimization: currently it simply iterates through all facts in the factbase in order to find those that match the provided terms. Obviously, even a simple indexing may significantly increase performance.

Here is how you use it (it's thread-safe, by the way):

fb =
f = fb.insert
f.kind = 'book'
f.title = 'Object Thinking'
fb.query('(eq kind "book")').each do |f|
  f.seen = true
fb.query('(not (exists seen))').each do |f|
  f.title = 'Elegant Objects'

You can save the factbase to the disc and then load it back:

file = '/tmp/simple.fb'
f1 =
f = f1.insert = 42, f1.export)
f2 =
assert(f2.query('(eq foo 42)').each.to_a.size == 1)

There are some boolean terms available in a query (they return either TRUE or FALSE):

  • (always) and (never) are "true" and "false"
  • (not t) inverses the t if it's boolean (exception otherwise)
  • (or t1 t2 ...) returns true if at least one argument is true
  • (and t1 t2 ...) returns true if all arguments are true
  • (when t1 t2) returns true if t1 is true and t2 is true or t1 is false
  • (exists k) returns true if k property exists in the fact
  • (absent k) returns true if k property is absent
  • (eq a b) returns true if a equals to b
  • (lt a b) returns true if a is less than b
  • (gt a b) returns true if a is greater than b
  • (many a) return true if there are many values in the a property
  • (one a) returns true if there is only one value in the a property
  • (matches a re) returns true when a matches regular expression re

There are a few terms that return non-boolean values:

  • (at i a) returns the i-th value of the a property
  • (size k) returns cardinality of k property (zero if property is absent)
  • (type a) returns type of a ("String", "Integer", "Float", or "Time")
  • (either a b) returns b if a is nil

Also, some simple arithmetic:

  • (plus a b) is a sum of a and b
  • (minus a b) is a deducation of b from a
  • (times a b) is a multiplication of a and b
  • (div a b) is a division of a by b

One term is for meta-programming:

  • (defn foo "self.to_s") defines a new term using Ruby syntax and returns true
  • (undef foo) undefines a term (nothing happens if it's not defined yet)

There are terms that are history of search aware:

  • (prev a) returns the value of a in the previously seen fact
  • (unique k) returns true if the value of k property hasn't been seen yet

There are also terms that match the entire factbase and must be used inside the (agg ..) term:

  • (count) returns the tally of facts
  • (max k) returns the maximum value of the k property in all facts
  • (min k) returns the minimum
  • (sum k) returns the arithmetic sum of all values of the k property

The agg term enables sub-queries by evaluating the first argument (term) over all available facts, passing the entire subset to the second argument, and then returning the result as an atomic value:

  • (lt age (agg (eq gender 'F') (max age))) selects all facts where the age is smaller than the maximum age of all women
  • (eq id (agg (always) (max id))) selects the fact with the largest id

How to contribute

Read these guidelines. Make sure you build is green before you contribute your pull request. You will need to have Ruby 3.2+ and Bundler installed. Then:

bundle update
bundle exec rake

If it's clean and you don't see any error messages, submit your pull request.